Zoom lens

ABSTRACT

This invention relates to a compact zoom lens. The zoom lens comprises of small number of elements arranged in three groups. The first group has negative refractive power, the second group has positive refractive power and the third group has negative refractive power. The air space between each of two adjacent groups is made variable to effect zooming.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to compact zoom lenses suitable for use in photographic devices.

2. Description Relative to the Prior Art

A number of kinds of zoom lenses are known for use in single lens reflex (SLR) cameras. Many such SLR camera lenses are so-called "short" zoom lenses that are comprised of a front negative component and a rear positive component. An example of such a zoom lens is disclosed in U.S. Pat. No. 4,198,128. Although this zoom lens itself is relatively short, it has a long back focal length. The long back focal length provides the necessary space in the SLR camera to allow for insertion of a mirror. However, the length from the first lens surface to the image forming or focal plane is relatively long. Thus, even though the lens itself may be short, a camera embodying the lens is inevitably bulky because of the long back focal length.

A non-SLR camera (sometimes called a "viewfinder" camera) does not require a long back focal length. There is thus an opportunity to provide a less bulky camera by designing a compact zoom lens with a short back focal length.

U.S. Pat. No. 4,936,661 describes a zoom lens having a short back focal length with negative, positive and negative units from front to rear. The negative unit closest to the image provides the majority of the change in focal length. In the less complex examples the front negative and positive units do not move relative to each other. In these examples the chromatic aberration could not be sufficiently corrected to get both a high aperture and a broad zoom range.

A zoom lens system disclosed in Japanese Kokai (unexamined Publication) No. 56-128,911, includes a first positive lens group and a second negative lens group which move relatively to vary the distance therebetween and to vary the focal length of the system for zooming. This zoom lens system, while being sufficiently short in overall length when adjusted for wide-angle photography, is limited to a zooming ratio of approximately 1.5, which is less than that usually available for an SLR camera.

Another zoom lens, disclosed in U.S. Pat. No. 4,787,718, comprises a first negative lens group, a second and a third positive lens group, and a rear negative lens group. It has a zooming ratio of about 2× and a sufficiently shortened overall length. This lens system has four moving groups, and although the distance between the first and third lens group is maintained during zooming, the two positive groups move at different speeds, and the relative distance between them changes. This zoom lens system has eight glass elements.

A zoom lens disclosed in U.S. Pat. No. 4,830,476 comprises two moving lens groups--a front positive lens group and a rear negative lens group. This zoom lens is relatively compact and has a zooming ratio of about 2×. Both the front group and the rear group have one positive and one negative lens element. Although this zoom lens has only four lens elements, in order to correct aberrations sufficiently, all five embodiments use at least three, and sometimes four, gradient index elements.

A zoom lens disclosed in U.S. Pat. No. 4,818,081 uses a configuration similar to the one disclosed in '476. As in '476, the front lens group of the lens system disclosed in U.S. Pat. No. '081 contains negative and positive subgroups which stay together during zooming. In addition, as in the zoom lens disclosed by '476, the rear zooming lens unit contains a positive, as well as a negative lens. This lens has a zooming range of 1.5 to 1.6× which is less than generally desirable for an SLR camera.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a compact zoom lens particularly suited for use in a non-SLR camera in which a zoom lens with relatively few optical elements is color corrected for the range of interest. Another object of the present invention is to produce a zoom lens with low manufacturing cost

According to the present invention, one or all of the above objects are accomplished by a zoom lens comprising three optical units movable for zooming and, having, from front to rear, negative, positive and negative powers, respectively. The change of magnification effected during zooming by the negative third optical unit is at least equal to, and preferably greater than, that of the positive optical unit. The power of the third optical unit (K₃) is approximately equal to the power of the system at the short focal length zoom position ##EQU1## This is because the third group is used mainly for correction of Petzval curvature and does not need to contribute power in the short focal length position, since K_(w) ≃K₁ +K₂, where K_(w) is the power of a zoom lens in a wide angle (or a short focal length) position and K_(i) is the power of the i^(th) optical unit power.

According to another aspect of the invention, the ratio of powers of the first to third optical units K₁ /K₃ is always larger than 0.6, preferably larger than 1.

According to a further preferred embodiment, the first negative optical unit has a front negative lens element. This ratio guarantees weaker power of the first group relative to the third group so that an extra element will not be needed for color correction. Because extra elements are not needed the resulting design is compact as well as inexpensive to make. In addition, weaker elements generally have larger tolerances and thus manufacturing is easier. As a consequence, the third optical unit can be of relatively simple construction because the effective aperture at the wide angle position can be small as a result of its close proximity to the image plane.

For many compact cameras, it is also desirable that the manufacturing cost be low. Thus according to a preferred embodiment of the invention, the zoom lens has few lens elements and uses plastic optical materials. In fact, according to a preferred embodiment, it has been found that a well corrected zoom lens can be designed with as few as three lens elements if such a three optical unit construction is employed in which a relatively strong first negative optical unit is followed by a positive second optical unit and a third negative optical unit. If the powers and optical materials are chosen correctly, chromatic aberrations can be corrected, even though the individual units are not color corrected.

It is an advantage of a preferred embodiment of the invention that the lens system can be color corrected without correcting each unit separately. However, this is a valuable feature when considering the limited available choice of optical plastic materials. For further aberration correction, for example, in designing extensions of zoom range, it is desirable to partially correct the color of the positive optical unit, for example by forming the positive unit of two or more elements.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 shows the outline of a zoom lens corresponding to a first illustrative embodiment of the present invention;

FIG. 2 shows the outline of a zoom lens corresponding to a second illustrative embodiment of the present invention;

FIG. 3 shows the outline of a zoom lens corresponding to a third illustrative embodiment of the present invention;

FIG. 4 shows the outline of a zoom lens corresponding to a fourth illustrative embodiment of the present invention;

FIG. 5 shows the outline of a zoom lens corresponding to a fifth illustrative embodiment of the present invention; and

FIG. 6 shows the outline of a zoom lens corresponding to a sixth illustrative embodiment of the present invention;

FIG. 7 shows the outline of a zoom lens corresponding to a seventh illustrative embodiment of the present invention;

FIG. 8 shows the outline of a zoom lens corresponding to an eighth illustrative embodiment of the present invention;

FIG. 9 shows the outline of a zoom lens corresponding to a ninth illustrative embodiment of the present invention;

FIG. 10 shows the outline of a zoom lens corresponding to a tenth illustrative embodiment of the present invention;

FIG. 11 shows the outline of a zoom lens corresponding to an eleventh illustrative embodiment of the present invention;

FIG. 12 shows the outline of a zoom lens corresponding to a twelfth illustrative embodiment of the present invention;

FIG. 13 shows the outline of a zoom lens corresponding to a thirteenth illustrative embodiment of the present invention;

FIG. 14 shows the outline of a zoom lens corresponding to a fourteenth illustrative embodiment of the present invention;

FIG. 15 shows the outline of a zoom lens corresponding to a fifteenth illustrative embodiment of the present invention;

FIG. 16 shows the outline of a zoom lens corresponding to a sixteenth illustrative embodiment of the present invention;

FIG. 17 shows the outline of a zoom lens corresponding to a seventeenth illustrative embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The lens systems in accordance with the present invention, in the form of an easily manufacturable compact zoom lens, comprise, from front-to-rear, a first, negative optical unit A axially movable for compensation, a second, positive optical unit B, axially movable for change in magnification, a third, negative optical unit C, axially movable for change in magnification, and in one of the illustrative embodiments, a fourth, fixed optical unit D. Focus control is achieved by moving either the optical unit A, or optical unit B, or both, as exemplified by the various embodiments. Color correction is achieved by distribution of negative power between the first and third optical units (A and C). The variable airspaces are denoted by letters VAS_(i), where subscript i is an integer from 1 to 4 and denotes the numerical order of the airspaces. For example, there is a variable airspace VAS₁ between the negative optical unit A and the positive optical unit, B, as well as another variable airspace VAS₂ between the positive optical unit B and the negative optical unit C to effect zooming between wide angle mode and telephoto mode of operation. In all of the embodiments the zooming spaces have been desensitized to aberration determination with zoom motion. The invention comprises several distinct species that will be described below in greater detail.

All linear dimensions in this Specification are millimeters unless specified otherwise.

The first zoom lens embodiment corresponding to the first species of the present invention is given a reference numeral 1 and is illustrated in FIG. 1. It comprises three optical units. This embodiment is illustrative of the species in which each of the optical units has only one lens element.

An important characteristic of this species is that while each optical unit has only one lens element, and while each of the optical units is not individually color corrected, the overall optical zoom lens system is color corrected.

The lens system includes a first, negative optical unit A₁, a second, positive optical unit B₁ and a third, negative optical unit C₁. As the focal length of the lens increases, all optical units move away from the film plane at different speeds. While the movements of the second and third optical units contribute to the change in magnification, the movement of the third optical unit C₁ is primarily responsible for that change. The aperture stop ST₁ position is fixed with respect to the second optical unit B₁, and is located between the second optical unit B₁ and the third optical unit C₁. The lens system is so structured that the effective focal length of the overall lens system is varied by changing, relative to each other, distance VAS₁ between the first and the second optical units A₁ and B₁, distance VAS₂ forming a part of the space between the second and the third optical units B₁ and C₁.

Each of the lens elements is plastic. Thus, aspheric surfaces can be manufactured relatively inexpensively Therefore, there is at least one aspheric surface per lens element.

The aspheric equation describing these surfaces is: ##EQU2## where X: is the distance along the optical axis

Y: is the height from an optical axis

C: is the vertex radius of curvature of a curved surface

K: is the Conic coefficient and

AD through AI: are aspheric coefficients of 4th, 6th, 8th, 10th, 12th and 14th order

The value of the terms AD, AE, AF, AG, AH, AI and K for the various surfaces are given in table 1b.

The first, front optical unit A₁ is in a form of a negative biconcave lens component. This lens component is a single lens element E102 having front and rear surfaces S₁ and S₂ and thickness T₁. Both the front surface S₁ and the rear surface S₂ are aspheric. The values of the radii of surfaces S₁ and S₂ and the value T₁, as well as the radii of the curvature and thicknesses of the rest of the elements are given in Table 1A. The values of aspheric coefficients are given in Table 1B.

A second optical unit B₁ is spaced from the first optical unit A₁, by a variable airspace VAS₁. The second optical unit B₁ has positive refractive power and is in a form of a single positive lens component. This lens component is a biconvex lens element E112 having front and rear surfaces S₃ and S₄ and thickness T₂. The front surface S₃ and the rear surface S₄ of the lens element E112 are also aspherical surfaces.

The third optical unit C₁ is spaced from the second optical unit B₁ by a variable airspace VAS₂. The third optical unit C₁ is negative and therefore consists of a negative lens component. This lens component is a single negative meniscus lens element E132 having a front and a rear radii S₅ and S₆ and a thickness T₃. The rear surface S₆ is aspherical.

This first embodiment varies from a focal length of 38.024 mm. and f/4.6 to a focal length of 65.208 mm and f/7.3. The ratio of powers of the first to the third optical unit is=1.6. The ratio of long focal length to the short focal length is 1.7. Table 1 gives various parameters of the lens illustrarted in FIG. 1A, including the radii of the surfaces S₁ to S₆ of the elements E102 to, E112 and E132. Table 1B gives values of the aspheric coefficients for surfaces S₁, S₂, S₃, S₄ and S₆. Table 1-C gives further parameters for the lens illustrated in FIG. 1.

                  TABLE 1-A                                                        ______________________________________                                                 VERTEX    THICK-            CLEAR                                      SURFACE RADIUS    NESS     GLASS    APERTURE                                   ______________________________________                                         S1      -15.32    1.300    KPOLYSTY  9.8                                       S2       717.58   VAS.sub.1          9.7                                       S3       20.98    4.229    ACRYLIC  10.3                                       S4      -12.44    3.145             11.1                                               ∞   2.614              9.7                                               ∞   VAS.sub.2         10.0                                       S5      -11.92    1.900    KPUV     18.1                                       S6      -28.44    VAS.sub.3         22.2                                               ∞   11.017            31.3                                       ______________________________________                                    

                  TABLE 1-B                                                        ______________________________________                                         POLYNOMIAL ASPHERS                                                             (COEFFICIENTS OF THE EVEN POWERED TERMS)                                       ______________________________________                                         SURFACE   AD (4TH)    AE (6TH)  AF (8TH)                                       ______________________________________                                         S1         4.897E-06   1.314E-08                                                                               2.788E-08                                      S2        -9.649E-05  -8.153E-08                                                                               9.231E-08                                      S3        -3.517E-04  -2.120E-06                                                                               -2.737E-07                                     S4        -1.248E-04  -2.725E-06                                                                               -1.316E-07                                     S6         1.448E-05  -2.657E-08                                                                               5.805E-12                                      ______________________________________                                         SURFACE   AG (10th)   AH (12TH) AI (14TH)                                      ______________________________________                                         S1        -1.214E-10  -2.570E-11                                                                               4.017E-13                                      S2        -2.214E-09  -6.570E-11                                                                               2.049E-12                                      S3         5.549E-10   2.859E-10                                                                               -1.156E-11                                     S4         1.831E-10   5.158E-11                                                                               -2.092E-12                                     S6         6.227E-14  -1.120E-14                                                                               6.029E-17                                      ______________________________________                                    

                  TABLE 1-C                                                        ______________________________________                                         ZOOM SPACING DATA                                                              POSITION                                                                               VAS.sub.1  VAS.sub.1                                                                              VAS.sub.2                                                                              EFL  F/#                                    ______________________________________                                         1       3.164      19.699                                                      .019                               38.02                                                                               4.6                                    2       2.338      15.034  12.062  50.01                                                                               5.8                                    3       1.597      11.612  28.960  65.21                                                                               7.3                                    ______________________________________                                    

FIG. 2 illustrates a second embodiment of the present invention and corresponds to the second species of the invention.

This second embodiment is generally similar to the first embodiment described above and illustrated in FIG. 1. In FIG. 2, the three optical units and the variable airspaces are given the same reference letters, but with a subscript "2" added. However, because the shape of lens elements and the number of elements differ from one embodiment to another, and from one species to another, distinct reference numerals are used for each lens element in each of the embodiments. Table 2A gives values for the various lens system parameters including radii of curvature, thickness elements and distances therebetween. This second illustrative embodiment includes four lens elements E202, E222, E224 and E232 arranged in three units A₂, B₂ and C₂. The aperture stop is located between the second optical unit B₂ and the third optical unit C₂. All three optical units move for zooming. Optical units A₂ and B₂ move for focusing. Thus, there are variable airspaces VAS₁ and VAS₂ between the first and second optical units A₂ and B₂ and the second and the third optical units B₂ and C₂, respectively. All of the elements are made of plastic. There is one aspheric surface per element. The values for aspheric coefficients are given in Table 2b.

As in the case of the first embodiment, in this second embodiment the front optical unit A₂ has a single negative lens element E202, and the third optical unit C₂ consists of a single negative biconcave lens element E232. However, the construction of the second optical unit B₂ of the second embodiment is different from the construction of the optical unit B₁ in the first embodiment. Optical unit B₂ is still not color corrected by itself, but it consists of two positive lens components, i.e., a biconvex lens element E222 and a biconvex lens element E224, rather than a single lens component. Splitting the optical power of the second optical unit among two or more positive components provides more aberration control and results in a better performance and a somewhat extended focal length. The quality of this lens is similar to those used in conventional 35 mm SLR cameras.

Table 2-C gives further parameters for the lens system illustrated in FIG. 2.

The ratio of the extreme focal length of the second embodiment is 68.8 mm:38.8 mm which qualifies the magnification range as 2:1.

                  TABLE 2-A                                                        ______________________________________                                                           THICK-            CLEAR                                      SURFACE RADIUS    NESS     GLASS    APERTURE                                   ______________________________________                                         S1      -18.804   1.300    KPOLYSTY 17.9                                       S2      117.174   VAS.sub.1         17.5                                       S3      16.353    3.900    ACRYLIC  16.1                                       S4      -34.328    .570             15.6                                       S5      44.251    3.400    ACRYLIC  13.7                                       S6      -55.618   VAS.sub.2         11.9                                               ∞   14.840             7.7                                       S7      -9.801    1.930    ACRYLIC  16.7                                       S8      -24.687   11.097            22.0                                       ______________________________________                                    

                  TABLE 2-B                                                        ______________________________________                                         POLYNOMIAL ASPHERS                                                             (COEFFICIENTS OF THE EVEN POWERED TERMS)                                       ______________________________________                                         SURFACE   AD (4TH)    AE (6TH)  AF (8TH)                                       ______________________________________                                         S2        -3.745E-05  -2.177E-07                                                                                2.162E-09                                     S3        -8.042E-05  -3.442E-07                                                                               -3.732E-10                                     S6         2.698E-05  -8.546E-07                                                                                1.232E-08                                     S8        -1.592E-05   5.291E-07                                                                               -8.063E-09                                     ______________________________________                                         SURFACE   AG (10TH)   AH (12TH) AI (14TH)                                      ______________________________________                                         S2        -4.515E-12  -1.463E-13                                                                                3.018E-16                                     S3         1.163E-11   3.655E-13                                                                               -6.877E-15                                     S6         5.410E-12  -5.623E-12                                                                                6.274E-14                                     8S         9.649E-12   5.651E-13                                                                               -3.282E-15                                     ______________________________________                                    

                  TABLE 2-C                                                        ______________________________________                                         ZOOM SPACING DATA                                                              POSITION                                                                               VAS.sub.1  VAS.sub.2                                                                              BFL     EFL  F/#                                    ______________________________________                                         1       2.882      13.935  11.0983 38.80                                                                               4.4                                    2       1.709      11.205  20.4615 50.08                                                                               5.6                                    3       .400       8.840   34.897  68.58                                                                               7.2                                    ______________________________________                                    

Tables 3A through 3C provide an additional example of the second species, and a third illustrative embodiment of the present invention.

The third illustrative embodiment, shown in FIG. 3, is very similar to the second illustrative embodiment illustrated in FIG. 2. The main difference between the second and the third illustrative embodiments is that the first movable front unit comprises two negative lens components, instead of a single negative lens component. The first lens component is a meniscus lens element oriented with its concave surface towards the second component. The second component is nominally biconcave, meaning that its vertex radii of curvature define a biconcave lens component. The third illustrative embodiment is a very compact 3× zoom lens with a minimum BFL at wide angle position of 17.3. As the focal length of the lens increases, all optical units move away from a film plane at different rates. The aperture stop moves with a second moving optical unit and maintains constant size throughout the zoom range. Because a first negative unit 301 of this embodiment consists of two negative lens elements a 3× magnification change or zoom range was achieved. However, at 3× it was difficult to correct for axial color at a wide angle position with only five elements, thus this design should be used with either a very narrow spectral band, or monochromatically. It is possible that a modified form of this five element design will work better for a zoom range shorter than 38-90.

                  TABLE 3-A                                                        ______________________________________                                                           THICK-   OPTICAL  CLEAR                                      SURFACE RADIUS    NESS     MATERIAL APERTURE                                   ______________________________________                                         S1      43.603    1.500    KPOLYSTY 14.4                                       S2      25.305    2.408             13.8                                       S3      -21.027   1.300    KPUV     13.8                                       S4      37,822    VAS.sub.1         14.3                                       S5      14.122    3.900    KACRYLIC 14.4                                       S6      -34.544    .149             14.5                                       S7      38.447    3.400    KACRYLIC 14.3                                       S8      -44.390   4.505             13.9                                               ∞   VAS.sub.2         10.4                                       S9      -8.580    1.930    KACRYLIC 14.6                                        S10    -14.985   63.225            18.3                                       ______________________________________                                    

                  TABLE 3-B                                                        ______________________________________                                         POLYNOMIAL ASPHERS                                                             (COEFFICIENTS OF THE EVEN POWERED TERMS)                                       ______________________________________                                         SURFACE   AD (4TH)    AE (6TH)  AF (8TH)                                       ______________________________________                                         S1        -1.877E-05  -1.303E-07                                                                               -7.509E-10                                     S4        -1.066E-04  -4.836E-07                                                                                2.081E-09                                     S5        -1.790E-04  -7.582E-07                                                                               -4.329E-09                                     S8        -2.344E-05  -1.263E-06                                                                                6.102E-09                                      S10       3.162E-07   3.960E-07                                                                               -9.166E-09                                     ______________________________________                                         SURFACE   AG (10TH)   AH (12TH) AI (14TH)                                      ______________________________________                                         S1        -2.246E-12  -7.946E-14                                                                               -5.693E-15                                     S4        -6.140E-11  -1.798E-12                                                                               -2.293E-14                                     S5        -2.996E-11  -8.389E-13                                                                               -5.785E-14                                     S8        -3.576E-11  -6.482E-12                                                                                8.306E-14                                      S10       4.786E-11   7.227E.13                                                                               -7.425E-15                                     ______________________________________                                    

                  TABLE 3-C                                                        ______________________________________                                         ZOOM SPACING DATA                                                              POSITION         VAS.sub.1                                                                              VAS.sub.2                                             ______________________________________                                         1                3.056   14.288                                                2                .999    9.179                                                 3                .400    7.931                                                 ______________________________________                                    

FIG. 4 illustrates a fourth illustrative embodiment and corresponds to the third species of the invention. In FIG. 4, the three moving optical units are given the same reference letters as their counterparts in the first embodiment described above and illustrated in FIG. 1, but with the subscript "4" added.

In this fourth embodiment, the first movable front optical unit A₄ includes a single negative lens component consisting of a single biconcave lens element E402, a movable optical unit B₄ includes a single positive lens component consisting of a biconvex lens element E422, and a third movable optical unit C₄ includes a negative lens component consisting of a meniscus lens element E432. The lens elements of the first three optical units are made of plastic and have at least one aspheric surface per each of the elements. In addition, there is a fourth, fixed positive optical unit D₄ located to the rear of the third optical unit C₄. The fourth, fixed optical unit D₄ consists of a single positive meniscus glass lens element E442. This fourth optical unit D₄ helps with aberration corrections, and it also helps to flatten the field. Table 4A gives values for various parameters of the lens illustrated in FIG. 4, including the radii of the elements and their thicknesses. Table 4B gives values for the aspheric coefficients describing the aspheric surfaces of the plastic lens elements.

                  TABLE4-A                                                         ______________________________________                                                           THICK-            CLEAR                                      SURFACE RADIUS    NESS     GLASS    APERTURE                                   ______________________________________                                         S1      -18.263   1.800    KPOLYSTY 12.4                                       S2      85.945    VAS.sub.1         11.8                                       S3      14.408    4.100    ACRYLIC  10.6                                       S4      -15.033   5.557             10.8                                               ∞   2.614             8.6                                                ∞   VAS.sub.2         9.5                                        S5      -9.976    1.900    KPUV     15.4                                       S6      -27.393   VAS.sub.3         19.7                                       S7      -42.700   3.000    F5       28.8                                       S8      -80.643   10.880            30.0                                       ______________________________________                                    

                  TABLE 4-B                                                        ______________________________________                                         POLYNOMIAL ASPHERS                                                             (COEFFICIENTS OF THE EVEN POWERED TERMS)                                       ______________________________________                                         SURFACE   AD (4TH)    AE (6TH)  AF (8TH)                                       ______________________________________                                         S2        -6.841E-05  1.856E-06 -4.992E-08                                     S3        -1.888E-04  -1.638E-07                                                                               -1.152E-07                                     S4        -3.319E-05  -1.008E-06                                                                               -1.047E-07                                     S6         1.880E-05  -1.166E-07                                                                                2.649E-09                                     ______________________________________                                         SURFACE   AG (10TH)   AH (12TH) AF (14TH)                                      ______________________________________                                         S2        -1.929E-10  4.135E-11 -6.148E-13                                     S3        -1.416E-09  1.221E-10 -3.332E-12                                     S4        -5.438E-11  4.885E-11 -1.466E-12                                     S6        -4.993E-11  3.791E-13 -1.053E-15                                     ______________________________________                                    

                  TABLE 4-C                                                        ______________________________________                                         ZOOM SPACING DATA                                                              POSITION                                                                               VAS.sub.1  VAS.sub.2                                                                              VAS.sub.3                                                                              EFL  F/#                                    ______________________________________                                         1       3.278      13.017  .600    38.004                                                                              4.4                                    2       1.885      11.380  9.010   49.998                                                                              5.6                                    3        .817      10.002  22.032  66.284                                                                              7.2                                    ______________________________________                                    

The ratio of powers of the first optical unit A₄ to the third optical unit C₄ is 1.2. The ratio of extreme focal length in the fourth embodiment is 66.38 or about 1.7:1

FIG. 5 illustrates the fifth embodiment of the present invention corresponding to the fourth species of the invention. As in the case of the first embodiment, in this fifth embodiment, the front optical unit A₅ has a single negative element E502, and the third optical unit C₅ consists of a single negative meniscus lens element E532. However, the second optical unit B₅ is different from the construction of the optical unit B₁ in the first embodiment. While the second optical unit B₁ of the first embodiment was not color corrected, the second optical unit B₅ of the fifth embodiment is color corrected. The second optical unit B₅ comprises a doublet component and consists of a biconvex lens element E522 and a negative meniscus lens element E524. Again, as in first embodiment, all of the lens elements are made of plastic.

The zooming motion of the front optical unit compared to the second optical unit B5 is quite small, therefore it may be possible to combine the two units for focusing. This would leave only two groups for the zooming system.

Tables 5A through 5C give the important parameters of the fifth embodiment.

                  TABLE 5-A                                                        ______________________________________                                                           THICK-            CLEAR                                      SURFACE RADIUS    NESS      GLASS   APERTURE                                   ______________________________________                                         S1      -33.479   1.300     ACRYLIC 18.4                                       S2      70.626    VAS.sub.1         17.2                                       S3      14.339    4.300     ACRYLIC 11.7                                       S4      -12.411    .037             10.9                                       S5      -12.102   2.315     591307  10.9                                       S6      -27.966   4.810             10.4                                               ∞   2.614             8.8                                                ∞   VAS.sub.2         9.5                                        S7      -9.498    3.159     ACRYLIC 16.7                                       S8      -17.758   31.850            21.9                                       ______________________________________                                    

                  TABLE 5-B                                                        ______________________________________                                         POLYNOMIAL ASPHERS                                                             (COEFFICIENTS OF THE EVEN POWERED TERMS)                                       ______________________________________                                         SURFACE   AD (4TH)    AE (6TH)   AF (8TH)                                      ______________________________________                                         S2        -1.200E-05  3.248E-08  9.423E-11                                     S3         2.159E-05  2.531E-07  -3.548E-10                                    S6         2.702E-05  -7.391E-07 4.572E-08                                     S8        -8.310E-06  -2.038E-07 2.104E-09                                     ______________________________________                                         SURFACE   AG (10TH)   AH (12TH)  AF (14TH)                                     ______________________________________                                         S2        -3.066E-11  6.035E-13  -3.432E-15                                    S3         1.236E-10  1.171E-12  5.420E-14                                     S6        -1.343E-09  3.069E-11  -2.479E-13                                    S8        -1.512E-11  4.339E-15  3.746E-17                                     ______________________________________                                    

                  TABLE 5-C                                                        ______________________________________                                         ZOOM SPACING DATA                                                              POSITION                                                                               VAS.sub.1  VAS.sub.2                                                                              BFL     EFL  F/#                                    ______________________________________                                         1       10.896     16.600  10.55   37.84                                                                               4.5                                    2       5.982      14.341  19.62   50.00                                                                               5.5                                    3       2.004      12.736  30.28   65.55                                                                               6.9                                    ______________________________________                                    

The ratio of the extreme focal length in the sixth embodiment is 1.7:1 which qualifies the magnification range as 2:1. The F1 number changes from f/6.9 to f/4.55.

FIG. 6 further illustrates the fourth species of the present invention. It corresponds to the sixth illustrative embodiment. The lens system of the sixth embodiment shown in FIG. 6 is similar to the lens system of the fifth embodiment shown in FIG. 5. The second, positive unit B₆ of sixth embodiment, is also in the form of a doublet. In the sixth illustrative embodiment, the doublet takes a form of a positive biconvex lens element E622 and a negative biconcave lens element E624. Due to the difference in refractive index of plastic materials used in the sixth, versus those used in the fifth embodiment, the relative size and form of corresponding elements in a second optical unit differ between the fifth and the sixth embodiments for example the lens embodiments comprising the second optical unit of the sixth embodiment are larger in diameter than those of the fifth embodiment. Tables 6A through 6C give the important parameters of the sixth illustrative embodiment.

                  TABLE 6-A                                                        ______________________________________                                                           THICK-   OPTICAL  CLEAR                                      SURFACE RADIUS    NESS     MATERIAL APERTURE                                   ______________________________________                                         S1      -37.78    1.800    591307   23.0                                       S2      147.99    VAS.sub.1         21.9                                       S3      10.72     6.198    ACRYLIC  16.2                                       S4      -45.24     .232             14.4                                       S5      -57.62    1.624    591307   13.4                                       S6      191.77     .000             11.3                                               ∞   6.067             11.6                                               ∞   VAS.sub.2          7.4                                       S7      -10.89    1.673    ACRYLIC  16.3                                       S8      -27.01    27.992            20.3                                       ______________________________________                                    

                  TABLE 6-B                                                        ______________________________________                                         POLYNOMIAL ASPHERS                                                             (COEFFICIENTS OF THE EVEN POWERED TERMS)                                       ______________________________________                                         SURFACE   AD (4TH)    AE (6TH)  AF (8TH)                                       ______________________________________                                         S3         1.156E-04   5.922E-07                                                                               2.566E-09                                      S6         1.510E-04   1.162E-06                                                                               3.713E-08                                      S8        -5.978E-07  -1.705E-07                                                                               2.776E-09                                      ______________________________________                                         SURFACE   AG (10TH)   AH (12TH) AF (14TH)                                      ______________________________________                                         S3         2.012E-10  -2.724E-12                                                                               2.023E-14                                      S6        -2.024E-09   7.949E-11                                                                               -1.025E-12                                     S8        -1.766E-11  -2.943E-14                                                                               4.735E-16                                      ______________________________________                                    

                  TABLE 6-C                                                        ______________________________________                                         ZOOM SPACING DATA                                                              POSITION  VAS.sub.1 VAS.sub.2                                                                              BFL    EFL   F/#                                   ______________________________________                                         1         11.553    14.658  10.55  37.70 4.6                                   2         5.898     13.171  17.69  50.00 5.5                                   3         1.812     11.844  26.43  65.14 6.9                                   ______________________________________                                    

FIG. 7 corresponds to the seventh illustrative embodiment. This embodiment is very similar to the fifth and sixth illustrative embodiments illustrated in FIGS. 5 and 6. Because these embodiments are very similar, further description will not be given, and for understanding of the seventh embodiment, reference is directed to the description of the fifth embodiment herein. Tables 7A through 7C give important parameters of the seventh embodiment.

                  TABLE 7-A                                                        ______________________________________                                                           THICK-            CLEAR                                      SURFACE RADIUS    NESS     GLASS    APERTURE                                   ______________________________________                                         S1      -39.892   1.800    ACRYLIC  23.9                                       S2      92.587    VAS.sub.1         22.3                                       S3      14.158    6.200    ACRYLIC  15.5                                       S4      -15.103    .036             15.5                                       S5      -14.886   3.590    591307   15.5                                       S6      -48.353    .000             15.5                                               ∞   4.856             10.0                                               ∞   VAS.sub.2          8.5                                       S7      -10.923   1.670    ACRYLIC  19.2                                       S8      -21.623   29.607            23.8                                       ______________________________________                                    

                  TABLE 7-B                                                        ______________________________________                                         POLYNOMIAL ASPHERS                                                             (COEFFICIENTS OF THE EVEN POWERED TERMS)                                       ______________________________________                                         SURFACE   AD (4TH)    AE (6TH)  AF (8TH)                                       ______________________________________                                         S2        -5.142E-06  -8.010E-08                                                                               2.796E-09                                      S3         4.428E-05  -5.124E-08                                                                               5.275E-09                                      S6         4.575E-05  -6.689E-07                                                                               5.842E-08                                      S8        -1.209E-06  -4.207E-07                                                                               4.878E-09                                      ______________________________________                                         SURFACE   AG (10TH)   AH (12TH) AF (14TH)                                      ______________________________________                                         S2        -4.484E-11   3.262E-13                                                                               -8.798E-16                                     S3         1.542E-10  -5.361E-12                                                                               5.166E-14                                      S6        -2.502E-09   6.113E-11                                                                               -6.073E-13                                     S8        -1.566E-11  -1.087E-13                                                                               5.703E-16                                      ______________________________________                                    

                  TABLE 7-C                                                        ______________________________________                                         ZOOM SPACING DATA                                                              POSITION  VAS.sub.1 VAS.sub.2                                                                              BFL    EFL   F/#                                   ______________________________________                                         1         15.938    20.160  11.003 38.799                                                                               4.55                                  2         10.030    17.851  19.013 49.989                                                                               5.50                                  3          3.290    16.499  29.607 68.613                                                                               6.90                                  ______________________________________                                    

FIG. 8 illustrates the eighth embodiment of the present invention and corresponds to the fifth species of the invention. Table 8 gives values for various parameters describing the eighth embodiment. The first optical unit A₈ and the last optical unit C₈ of the eighth embodiment are similar to those of the first embodiment, A₁ and C₁. The second optical unit B₈ of the eighth embodiment is different from the second optical unit B₁ of the first embodiment. The second optical unit B₁ of the first embodiment was not color corrected. The second optical unit of the fifth embodiment is color corrected. The second optical unit B₁ of the first embodiment consists of a single positive lens element. The second optical unit B₈ consists of two positive lens components-a single positive lens element E822 and a cemented doublet. The cemented doublet consists of a biconcave lens element E824 and a negative biconcave lens element E826 cemented to it. Tables 8A-8C give values for various parameters describing the eighth embodiment.

                  TABLE 8-A                                                        ______________________________________                                                             THICK-           CLEAR                                     SURFACE RADIUS      NESS      GLASS  APERTURE                                  ______________________________________                                         S1      -51.163     1.700     NBFD11 26.3                                      S2       146.318    VAS.sub.1        25.4                                      S3      -34.987     3.769     LAC12  21.4                                      S4      -17115.910  13.982           20.5                                      S5       14.296     4.939     BSC7   10.3                                      S6      -14.296     1.000     FL7    9.3                                       S7       92.255     1.876            8.9                                               ∞     1.614            8.3                                               ∞     VAS.sub.2        7.9                                       S8       -8.671     1.900     FC5    15.0                                      S9      -15.783     35.010           19.0                                      ______________________________________                                    

                  TABLE 8-B                                                        ______________________________________                                         ZOOM SPACING DATA                                                              POSITION  VAS.sub.1 VAS.sub.2                                                                              BFL    EFL   F/#                                   ______________________________________                                         1         12.341    12.939  15.403 38.804                                                                               4.60                                  2         6.662     11.611  23.357 50.006                                                                               5.60                                  3         .590      10.869  35.010 68.638                                                                               7.20                                  ______________________________________                                    

Illustrative embodiments numbers nine through sixteen are very similar to the eighth illustrative embodiment and are shown in FIGS. 9-13. Tables 9 through 16 provide the important parameters for the above-mentioned embodiments.

                  TABLE 9-A                                                        ______________________________________                                                           THICK-            CLEAR                                      SURFACE RADIUS    NESS     GLASS    APERTURE                                   ______________________________________                                         S1      -19.489   1.000    NBFD10   15.8                                       S2      -57.315   1.100             15.7                                       S3      -16.491   1.000    FC5      15.8                                       S4      -54.054   VAS.sub.1         16.1                                       S5      46.985    2.700    F8       16.4                                       S6      -19.197    .200             16.4                                       S7      15.360    3.000    BSC7     13.4                                       S8      -16.215   2.500    FD6      13.4                                       S9      -53.873   VAS.sub.2         11.6                                               ∞   VAS.sub.3         6.1                                         S10    -10.944   1.200    ACRYLIC  14.8                                        S11    -30.947   VAS.sub.4         18.8                                               ∞   5.001             33.1                                       ______________________________________                                    

                  TABLE 9-B                                                        ______________________________________                                         POLYNOMIAL ASPHERS                                                             (COEFFICIENTS OF THE EVEN POWERED TERMS)                                       SURFACE  AD (4TH)  AE (6TH)  AF (8TH)                                                                               AG (10TH)                                 ______________________________________                                         10       -8.197E-05                                                                               -1.149E-06                                                                               6.871E-09                                                                              2.958E-10                                 ______________________________________                                    

                  TABLE 9-C                                                        ______________________________________                                         ZOOM SPACING DATA                                                              POSITION VAS.sub.1                                                                              VAS.sub.2                                                                              VAS.sub.3                                                                            VAS.sub.4                                                                            EFL   F/#                                 ______________________________________                                         1        3.063    .276   15.800                                                                                6.000                                                                               29.000                                                                               6.2                                 2        2.039   7.690    4.854                                                                               16.946                                                                               38.606                                                                               5.8                                 3        2.541   3.119   11.377                                                                               10.423                                                                               33.002                                                                               6.3                                 ______________________________________                                    

The lens system design represented by Tables 9A and 9B is a 1.4× zoom lens. This lens system, corresponding to the ninth embodiment has six lens elements arranged into three optical units. The first optical unit A₉ contains two negative meniscus lens elements E902 and E904. The concave surface of the lens elements E902 and E904 are oriented towards the object side. The first optical unit A₉ is followed by a second optical unit B₉. The optical unit B₉ is color corrected and contains two lens components. The first lens component of the second optical unit B₉ is a biconvex lens element E922, the second optical component is a cemented doublet. It consists of a biconvex lens element E924 cemented to a meniscus lens element E926. The second optical unit B₉ is followed by a third optical unit C₉. The third optical unit C₉ contains a single negative meniscus lens element E932, oriented with its concave surface towards the object side. This design is of the type where the aperture stop is positioned stationary relative to the image plane between the second zooming optical unit B₉ and the third zooming optical unit C₉. As a result the F-number varies from F/6.2 at the wide angle to F/5.8 at the longest focal length. Since the variation of the lens speed with zooming is so small, it can probably be assumed that for all the practical purposes the maximum F-number of the lens is constant. Consequently, one of the advantages of a camera utilizing this design is that the exposure determination can be done in a very simple fashion. Since the maximum speed of the lens at the wide angle is only F/6, the correction of the spherical aberation is easily achieved. The astigmatism and the tangential field are corrected by using an asphere on the rear element of the lens system.

                  TABLE 10-A                                                       ______________________________________                                                           THICK-            CLEAR                                      SURFACE RADIUS    NESS     GLASS    APERTURE                                   ______________________________________                                         S1      -18.012   1.000    TAF3     15.5                                       S2      474.104   VAS.sub.1         15.4                                       S3      58.005    2.700    FL7      15.3                                       S4      -19.016    .200             15.3                                       S5      13.636    3.000    FC5      12.6                                       S6      -20.931   2.500    FD6      12.1                                       S7      -104.385  VAS.sub.2         10.3                                               ∞   VAS.sub.3         6.4                                        S8      -10.036   1.200    ACRYLIC  14.8                                       S9      -23.395   VAS.sub.4         18.9                                               ∞   4.999             33.7                                       ______________________________________                                    

                  TABLE 10-B                                                       ______________________________________                                         POLYNOMIAL ASPHERS                                                             (COEFFICIENTS OF THE EVEN POWERED TERMS)                                       ______________________________________                                         SURFACE   AD (4TH)    AE (6TH)  AF (8TH)                                       ______________________________________                                         S8        -9.612E-05  -1.974E-06                                                                               3.889E-08                                      ______________________________________                                         SURFACE                                                                        NO.       AG (10TH)   AH (12TH) AI (14TH)                                      ______________________________________                                         S8        -7.506E-10   0.000E+00                                                                               0.000E+00                                      ______________________________________                                    

                  TABLE 10-C                                                       ______________________________________                                         ZOOM SPACING DATA                                                              POSI-                                                                          TION   VAS.sub.1                                                                              VAS.sub.2                                                                               VAS.sub.3                                                                            VAS.sub.4                                                                             EFL   F/#                                 ______________________________________                                         1      5.906    .137    16.800                                                                                6.000 28.100                                                                               6.20                                2      4.562   7.453     6.262                                                                               16.538 38.598                                                                               5.79                                3      5.267   2.985    12.412                                                                               10.389 32.999                                                                               6.30                                ______________________________________                                    

FIG. 10 illustrates the tenth embodiment. This embodiment is similar to the ninth embodiment described above with one exception, it has only five lens elements instead of six. In addition the rearmost lens element has an aspheric surface to facilitate the correction of aberrations.

                  TABLE 11-A                                                       ______________________________________                                                                             CLEAR                                      SURFACE RADIUS   THICKNESS   GLASS  APERTURE                                   ______________________________________                                         S1      -25.413  1.000       LACL6  12.9                                       S2      539.321  1.100              12.0                                       S3      -18.363  1.000       FC5    12.0                                       S4      172.107  VAS.sub.1          11.5                                       S5      29.116   1.933       BSC7   10.9                                       S6      -17.823   .200              10.8                                       S7      12.308   2.600       BACD5  9.2                                        S8      -14.030  5.440       NBFD10 8.4                                        S9      -83.692   .392              6.8                                         S10    ∞  VAS.sub.2          7.1                                         S11    -6.747   1.200       FC5    12.7                                        S12    -12.213  VAS.sub.3          16.6                                        S13    ∞  5.003              34.2                                       ______________________________________                                    

                  TABLE 11-B                                                       ______________________________________                                         ZOOM SPACING DATA                                                              POSITION VAS.sub.1                                                                               VAS.sub.2                                                                               VAS.sub.3                                                                             EFL    F/#                                   ______________________________________                                         1        1.785    11.865    6.572 29.003 4.60                                  2         .587    10.283   14.819 38.607 5.79                                  3        1.209    11.114   10.049 33.004 5.11                                  ______________________________________                                    

Tables 11A through 11B provide the numerical data for the lens system corresponding to the eleventh illustrative embodiment. The lens system has six glass elements and its focal length ranges between 29 and 39 mm. The configuration is very similar to the lens system configuration of the ninth embodiment in terms of number of lens elements, their shapes and their arrangement into the optical units. However, in this configuration the aperture stop moves with the second zoom group and the diameter of the aperture stop is maintained at constant value. The maximum f-number of this lens system varies from F/4.5 at the wide angle to f/5.6 at the longest focal length. This lens system contains no aspherical surfaces.

                  TABLE 12-A                                                       ______________________________________                                                           THICK-            CLEAR                                      SURFACE RADIUS    NESS     GLASS    APERTURE                                   ______________________________________                                         S1      -23.281   1.000    LAC8     12.0                                       S2      -77.986   1.100             11.4                                       S3      -18.509   1.000    FC5      11.0                                       S4      125.143   VAS.sub.1         10.4                                       S5      66.113    1.933    BAF3     9.4                                        S6      -19.864    .200             9.0                                        S7      13.664    3.000    BSC7     8.2                                        S8      -13.716   2.500    FD6      7.6                                        S9      -32.071    .500             7.5                                                ∞   VAS.sub.2         7.8                                         S10    -7.949    1.200    ACRYLIC  14.6                                        S11    -13.964   VAS.sub.3         18.5                                               ∞   4.100             34.3                                       ______________________________________                                    

                  TABLE 12-B                                                       ______________________________________                                         POLYNOMIAL ASPHERS                                                             (COEFFICIENTS OF THE EVEN POWERED TERMS)                                       ______________________________________                                         SURFACE                                                                        NO.       AD (4TH)     AE (6TH)  AF (8TH)                                      ______________________________________                                         11        -1.575E-05   -3.731E-07                                                                               0.000E+00                                     ______________________________________                                         SURFACE                                                                        NO.       AG (10TH)    AH (12TH) AF (14TH)                                     ______________________________________                                         11        0.000E+00    0.000E+00 0.000E+00                                     ______________________________________                                    

                  TABLE 12-C                                                       ______________________________________                                         ZOOM SPACING DATA                                                              POSITION   VAS.sub.1    VAS.sub.2                                                                              VAS.sub.3                                      ______________________________________                                         1          2.351        15.657  6.000                                          2           .963        13.467  15.066                                         3          1.689        14.601  9.843                                          ______________________________________                                    

The twelfth illustrative embodiment illustrated on FIG. 12 and represented by Tables 12A through 12C is very similar to the eleventh illustrative embodiment. It has the same number of lens elements, the lens elements are shaped similarly and their arrangements into optical units are similar to that of the eleventh embodiment. As in the tenth embodiment, the aperture stop moves with the second optical unit and its diameter is maintained constant. The only significant difference between the eleventh and twelfth illustrative embodiment is that the twelfth embodiment has five glass and one plastic lens element. The plastic lens element is a rear lens element. One of the surfaces of the rear lens element is aspherical to fascilitate the correction of aberations.

                  TABLE 13-A                                                       ______________________________________                                                            THICK-           CLEAR                                      SURFACE RADIUS     NESS     GLASS   APERTURE                                   ______________________________________                                         S1      -25.300    1.300    LAC8    16.0                                       S2      ∞    VAS.sub.1        15.5                                       S3      -174.280   2.600    FC5     13.2                                       S4      -21.220    VAS.sub.2        12.8                                       S5      14.620     3.500    LACL6   10.7                                       S6      -23.770    1.000    NBFD10  10.1                                       S7      137.500    3.060            9.8                                                ∞    VAS.sub.3        8.8                                        S8      -8.285     1.600    FC5     14.6                                       S9      -13.377    VAS.sub.4        17.8                                               ∞    6.900            35.1                                       ______________________________________                                    

                  TABLE 13-B                                                       ______________________________________                                         ZOOM SPACING DATA                                                              POSITION VAS.sub.1                                                                              VAS.sub.2                                                                              VAS.sub.3                                                                            VAS.sub.4                                                                            EFL   F/#                                 ______________________________________                                         1        6.318   1.539   15.357                                                                               10.333                                                                               39.000                                                                               4.60                                2        2.203   1.539   14.165                                                                               20.033                                                                               53.000                                                                               5.79                                3        4.608   1.539   14.759                                                                               14.022                                                                               44.000                                                                               5.03                                4        7.539    .311   15.357                                                                               10.333                                                                               36.512                                                                               4.43                                5        3.510    .232   14.165                                                                               20.033                                                                               48.507                                                                               5.50                                ______________________________________                                    

FIG. 13 illustrates the thirteenth embodiment of the present invention. Tables 13-A and 13-B provide important parameters of the lens system of this embodiment. The thirteenth embodiment is a five lens element, 1.4 zoom lens system. The F-number of the lens system varies from F/4.5 to F/5.6, and the focal length varies between 38 to 55 mm. This lens system has an internal focusing, i.e., focusing is accomplished by moving the first element of the second optical unit towards the film plane.

                  TABLE 14-A                                                       ______________________________________                                                                             CLEAR                                      SURFACE RADIUS   THICKNESS   GLASS  APERTURE                                   ______________________________________                                         S1      -32.554  1.300       BAC05  19.6                                       S2      55.013   VAS.sub.1          18.4                                       S3      113.511  2.700       TAF1   16.1                                       S4      -31.761  VAS.sub.2          15.7                                       S5      12.136   3.700       FC5    11.7                                       S6      -29.225  1.000       FD2    10.3                                       S7      38.755   3.348              9.5                                                ∞  VAS.sub.3          8.2                                        S8      -8.541   1.200       LAC8   15.4                                       S9      -14.147   .200              19.3                                        S10    310.334  4.400       FL7    26.5                                        S11    -48.348  VAS.sub.4          28.2                                               ∞  6.909              35.3                                       ______________________________________                                    

                  TABLE 14-B                                                       ______________________________________                                         POSI-                                                                          TION   VAS.sub.1                                                                              VAS.sub.2                                                                               VAS.sub.3                                                                            VAS.sub.4                                                                             EFL   F/#                                 ______________________________________                                         1      7.228   1.558    15.366                                                                                4.100 36.201                                                                               4.5                                 2      1.913   1.558    13.534                                                                               16.614 53.005                                                                               5.8                                 3      8.559    .227    15.366                                                                                4.100 33.534                                                                               4.3                                 4      3.252    .227    13.534                                                                               16.614 47.794                                                                               5.5                                 5      4.362   1.558    14.109                                                                               10.378 44.010                                                                               5.1                                 ______________________________________                                    

The fourteenth illustrative embodiment, shown in FIG. 14 is similar to the thirteenth embodiment. Tables 14a and 14b provide the important data.

The lens system of the fourteenth embodiment includes a front, negative power optical unit A14 movable for zooming, a second optical unit B14 of positive power movable for zooming and a third optical unit C14 of negative power also movable for zooming. The front optical unit A14 consists of a single biconcave lens element E1402. The second optical unit consists of two subunits, front and rear respectively. The front subunit is a single positive biconvex lens element E1422. The front subunit, moves towards the film plane for focusing. The rear subunit is a cemented doublet component. It consists of a biconvex positive lens element E1424 cemented to a biconcave lens element E1426. Both subunits move forward for zooming. The third optical unit has two lens components--a front component is a negative meniscus lens element E1432 and the rear component is a positive biconvex lens element E1434.

                  TABLE 15-A                                                       ______________________________________                                                                             CLEAR                                      SURFACE RADIUS   THICKNESS   GLASS  APERTURE                                   ______________________________________                                         S1      -21.860  1.300       TAF1   15.4                                       S2      -231.770 VAS.sub.1          14.9                                       S3      -4330.810                                                                               2.700       CF6    12.3                                       S4      -21.296   .200              11.8                                       S5      18.105   3.400       BAC4   10.5                                       S6      -20.362  1.000       FD1    10.1                                       S7      -259.226 1.000              9.8                                                ∞  VAS.sub.2          9.5                                        S8      -10.849  1.600       ACRYLIC                                                                               18.6                                       S9      -21.349  VAS.sub.3          23.1                                        S10    ∞  6.898              34.8                                       ______________________________________                                    

                  TABLE 15-B                                                       ______________________________________                                         POLYNOMIAL ASPHERS                                                             (COEFFICIENTS OF THE EVEN POWERED TERMS)                                       ______________________________________                                         SURFACE                                                                        NO.       AD (4TH)     AE (6TH)  AF (8TH)                                      ______________________________________                                         S8        -1.767E-05   -8.812E-08                                                                               -1.331E-09                                    ______________________________________                                         SURFACE                                                                        NO.       AG (10TH)    AH (12TH) AI (14TH)                                     ______________________________________                                         S9         1.097E-11   -1.726E-13                                                                                1.309E-15                                    ______________________________________                                    

                  TABLE 15-C                                                       ______________________________________                                         ZOOM SPACING DATA                                                              POSITION VAS.sub.1                                                                               VAS.sub.2                                                                               VAS.sub.3                                                                             EFL    F/#                                   ______________________________________                                         1        7.193    23.607    4.100 36.215 4.53                                  2        3.896    19.716   18.940 53.012 6.20                                  3        5.393    21.479   11.079 44.008 5.30                                  ______________________________________                                    

Tables 15A through 15C provide yet another example of the fifth species with internal focusing. FIG. 15 illustrates that the lens system has five elements E1502 through E1532, arranged in three optical units A₁₅, B₁₅, and C₁₅. This lens system has four glass and one plastic lens elements. The plastic lens element has an aspheric surface. As in the previous embodiment, all three optical units move differentially during zooming, and one of the subunits of the second optical unit is moved for focusing.

                  TBALE 16-A                                                       ______________________________________                                                                             CLEAR                                      SURFACE RADIUS   THICKNESS   GLASS  APERTURE                                   ______________________________________                                         S1      -35.148  1.300       PCD2   22.3                                       S2      61.193   VAS.sub.1          20.8                                       S3      75.049   3.600       F5     18.2                                       S4      -31.097  VAS.sub.2          17.6                                       S5      11.907   4.000       PCD2   12.4                                       S6      -32.563  1.000       FD13   10.3                                       S7      32.563   2.402              8.8                                                ∞  VAS.sub.3          7.7                                        S8      -7.833   1.200       LAC14  14.4                                       S9      -13.430   .200              18.6                                        S10    1405.963 3.800       FD1    26.1                                        S11    -52.074  VAS.sub.4          27.7                                               ∞  6.895              34.8                                       ______________________________________                                    

                  TABLE 16-B                                                       ______________________________________                                         ZOOM SPACING DATA                                                              POSITION   VAS.sub.1                                                                              VAS.sub.2  VAS.sub.3                                                                            VAS.sub.4                                  ______________________________________                                         1          7.320   1.908      13.758                                                                                5.613                                     2           .945   1.908      12.554                                                                               16.458                                     3          9.001    .227      13.758                                                                                5.613                                     4          2.598    .227      12.554                                                                               16.458                                     5          3.857   1.908      12.947                                                                               10.940                                     ______________________________________                                    

Because embodiment number 16 is very similar to the 14th embodiment, i.e., elements type, their form and their arrangement in optical units is the same as the elements to which they correspond in the fourteenth embodiment illustrated in FIG. 14, and since A is also similar to the fifteenth embodiment described herein, further description will not be given, an understanding of this embodiment, reference is directed to the description of the fourteenth and fifteenth embodiment herein.

                  TABLE 17-A                                                       ______________________________________                                                                             CLEAR                                      SURFACE RADIUS   THICKNESS   GLASS  APERTURE                                   ______________________________________                                         S1      -66.552  2.000       FC5    24.7                                       S2      59.653   VAS.sub.1          22.6                                       S3      15.733   5.000       CF6    8.9                                        S4      -12.148  1.000       FD15   8.2                                        S5      -35.063  1.809              8.2                                                ∞  2.614              7.7                                        S6      ∞  VAS.sub.2          7.1                                        S7      -9.251   1.900       FC5    15.5                                       S8      -16.393  32.448             19.0                                       ______________________________________                                    

                  TABLE 17-B                                                       ______________________________________                                         ZOOM SPACING DATA                                                              POSITION         VAS.sub.1                                                                              VAS.sub.2                                             ______________________________________                                         1                26.462  17.149                                                2                16.958  16.107                                                3                10.480  15.429                                                ______________________________________                                    

FIG. 17 illustrates the sixth species of the invention and corresponds to the seventeenth embodiment of the present invention. The sixth species of the present invention are similar to the fourth species, the only difference, being that glass was used instead of plastic and fewer aspheres were utilized. The ratio of powers of the first optical and to the third optical unit is 0.74. Tables 17A-C provides important parameters of the embodiment illustrated in FIG. 17.

The invention has been described in detail with particular reference to a presently preferred embodiment, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 

What is claimed is:
 1. A zoom lens comprising in order from an object side three optical units movable for zooming, a first optical unit that is negative, a second optical unit that is positive, and a third optical unit that is negative, in which said third optical unit provides a greater amount of the magnification change during zooming than provided by either of the first or the second optical unit and the third optical unit consists of a single negative lens element, and the ratio of powers of said first optical unit to said third optical unit of said zoom lens is between 0.7 and 1.6.
 2. A zoom lens according to claim 1 in which the second optical unit is a single element.
 3. A zoom lens according to claim 1 in which the second optical unit has no negative lens components.
 4. A zoom lens according to claim 1 and further including a non-movable positive optical unit located nearest an image plane.
 5. A zoom lens according to claim 1 in which the second optical unit consists of a singlet and a doublet.
 6. A zoom lens according to claim 1, wherein the first, negative optical unit consists of a single negative lens element having a concave surface facing towards the object side of said zoom lens.
 7. The zoom lens according to claim 1 and wherein the first optical unit consists of two negative lens components.
 8. The zoom lens according to claim 7 and wherein a first lens component of said two negative lens components is a meniscus lens oriented with its concave surface towards a second lens component of said two negative lens components.
 9. The zoom lens according to claim 7 and wherein the two negative lens components comprise two negative meniscus lens elements with the concave surfaces of said two meniscus lens elements oriented towards said object side.
 10. The zoom lens according to claim 9 and wherein said second optical unit comprises a biconvex lens element and a doublet of positive power.
 11. The zoom lens according to claim 7 and wherein a first of said two negative lens components consists of a single negative lens element with a concave surface of said single negative lens element facing said object side.
 12. The zoom lens according to claim 11 and wherein the second optical unit comprises two positive optical components.
 13. The zoom lens according to claim 12 and wherein a first component of said two positive optical components consists of a single positive lens element and a second component of said two positive optical components consists of a positive doublet.
 14. The zoom lens according to claim 11 wherein said single negative lens element is a meniscus lens element.
 15. A zoom lens comprising three optical units movable for zooming, a negative front optical unit, a positive middle optical unit, and a negative rear optical unit, in which said rear optical unit provides a greater amount of the magnification change during zooming than provided by either of the front or the middle optical unit and the front and rear optical units each consists of a single negative lens component, and the ratio of powers of said front optical unit to said rear optical unit is between 0.7 and 1.6 and in which said lens component of said rear optical unit consists entirely of a single negative element in which one surface of said element is aspherical.
 16. A zoom lens comprising three optical units movable for zooming, a negative front optical unit, a positive middle optical unit and a negative rear optical unit, in which said rear optical unit provides a greater amount of the magnification change during zooming than provided by either of the front or the middle optical unit, the ratio of powers of said front optical unit to said rear optical unit is between 0.7 and 1.6 and in which said rear unit consists of a negative lens element and a biconvex positive lens element.
 17. A zoom lens comprising:a front lens optical unit of negative power movable along an optical axis for zooming; a middle optical unit including two subunits each of positive power which move unitedly along the optical axis for zooming, one of the two subunits being movable along the optical axis for focusing; a rear optical unit on the image side of the front and middle optical units, the rear optical unit including only one negative element, said negative element being convex to the rear, said rear unit being movable along the optical axis for maintaining a fixed focal plane during zooming.
 18. A zoom lens system comprising three optical units movable for zooming, a negative first optical unit, a positive second optical unit and a negative third optical unit, in which said third optical unit provides a greater amount of the magnification change during zooming than provided by either of the first or the second optical unit and the third optical unit consists of a single negative lens element, and the ratio of powers of said first optical unit to said third optical unit is between 0.7 and 1.6 and wherein the power of the third optical unit relates to the power of the system at the short focal length zoom position, so that: ##EQU3## wherein K₃ is the power of the 3rd optical unit and K_(w) is the power of the lens system at the short focal length zoom position.
 19. A zoom lens according to claim 18 in which the second optical unit consists of a single lens element.
 20. A zoom lens according to claim 18 in which the second optical unit has no negative lens component.
 21. A zoom lens according to claim 18 and further including a non-movable positive optical unit that is located nearest an image plane.
 22. A zoom lens according to claim 18 in which the second optical unit is comprised of a singlet and a doublet.
 23. A zoom lens according to claim 18, wherein the first optical unit consists of a single negative lens element having a concave surface facing towards the object side of said zoom lens system.
 24. A zoom lens according to claim 18 in which said third optical unit consists of a negative lens element in which one surface of said element is aspherical.
 25. A zoom lens comprising, in order from an object side, three optical units movable for zooming, a first optical unit that is negative, a second optical unit that is positive, and a third optical unit that is negative, in which said third optical unit provides a greater amount of magnification change during zooming than provided by either of the first or the second optical unit and the first optical unit consists of a single negative lens element, and the ratio of powers of said first optical unit to said third optical unit of said zoom lens is between 0.7 and 1.6.
 26. The zoom lens according to claim 25 and wherein the second optical unit consists of a single lens element.
 27. The zoom lens according to claim 25 and wherein the third optical unit consists of a single lens element.
 28. The zoom lens according to claim 27 and wherein the second optical unit consists of a single lens element.
 29. The zoom lens according to claim 28 and further including a fourth fixed optical unit located to the rear of the third optical unit, said fourth unit consisting of a single positive lens element.
 30. The zoom lens according to claim 29 and wherein the lens element of the first optical unit is a biconcave lens element, the lens element of the second optical unit is a biconvex lens element and the lens element of the third optical unit is a meniscus lens element.
 31. The zoom lens according to claim 28 and wherein the lens element of the first optical unit is a biconcave lens element, the lens element of the second optical unit is a biconvex lens element and the lens element of the third optical unit is a meniscus lens element.
 32. The zoom lens according to claim 27 and wherein the single lens element of the third optical unit is a meniscus lens element.
 33. The zoom lens according to claim 32 and wherein the single lens element of the third optical unit has an aspherical surface which faces away from said object side.
 34. The zoom lens according to claim 32 and wherein the second optical unit is a doublet that consists of a biconvex lens element and a negative meniscus lens element.
 35. The zoom lens according to claim 32 and wherein the second optical unit is a doublet that consists of a positive biconvex lens element and a negative biconcave lens element.
 36. The zoom lens according to claim 32 and wherein the second optical unit consists of two positive lens components, wherein a first component of said lens components is a single positive lens element and a second component of said lens components is a doublet.
 37. The zoom lens according to claim 36 and wherein the first of said lens components is movable relative to said second component for internal focusing.
 38. The zoom lens according to claim 27 and wherein the second optical unit comprises two positive lens components.
 39. The zoom lens according to claim 38 and wherein the single lens element of the third optical unit is a meniscus lens element.
 40. The zoom lens according to claim 39 and wherein the single lens element of the third optical unit has an aspherical surface which faces away from said object side.
 41. The zoom lens according to claim 25 and wherein the lens element of the first optical unit is a biconcave lens element, the second optical unit consists of two components, wherein a first of said two components is a biconvex lens element and a second of said two components in a doublet.
 42. The zoom lens according to claim 41 and wherein both of said two components move for zooming and the first component moves relative to the second component for focusing.
 43. The zoom lens according to claim 42 and wherein the third optical unit comprises two lens components, wherein a first component of said two lens components of said third optical unit comprises a negative meniscus lens element and a second component of said two lens components of said third optical unit comprises a positive biconvex lens element. 